The fuel tank of an aircraft is generally placed in the empty volume of a box structure, particularly in the wing structure. In order to contain fuel, said volume must be sealed and also, the materials that make up said box structure must be protected from possible damage due to contact with fuel. That last characteristic is particularly relevant when the materials making up the box structure are composite materials with an organic matrix, on which fuel hydrocarbons act as solvents.
According to the prior art, such protection can be obtained by inserting a bag in the empty volume of the box structure used as a tank. This solution is unfavorable for aeronautics applications as the bag constitutes additional mass. Further, the internal shape of the empty volume, which is essentially determined by structural considerations, can be complex and both the adaptation of the shape of the bag to the volume and the introduction of said bag in the volume are difficult.
Another solution of the prior art consists in painting the structural parts that demarcate the empty volume of the box structure with special primer that is resistant to hydrocarbons. This technical solution requires a painting operation in the manufacturing sequence and its quality of performance depends on the know-how of the operator.
Finally, in a third solution of the prior art, protection is provided by applying liquid filler made of polythioether on the inside of the empty volume of the assembled box structure. This operation, which is generally carried out with a brush, is commonly called churning, and happens to be particularly difficult to carry out.
The document WO 2007 045466 describes a fuel tank in composite material with an organic matrix, and methods for manufacturing such a tank. The fuel tank described in this document of the prior art is designed for a motorcycle or automotive vehicle and is a small tank. The document discloses two embodiments of such a tank, the first consisting in molding an enclosure made up of thermoplastic material on which reinforced plies are then laid up. The second embodiment consists in first making an enclosure of layered composite material and then covering, after curing, the inside of the enclosure with thermoplastic film by blowing or rotary molding the film inside the volume of the tank made up in this way. These embodiments are totally unsuitable for making a tank intended for an aircraft.